1. Field of the Invention
The present invention generally relates to a waste water treatment process and, more particularly, to a process for treating raw liquid waste which contains organic matter which is dissolved and/or suspended in the liquid.
2. Description of the Prior Art
The problems facing municipalities in treating raw sewage, which is one form of waste water, are well known. The sewage consists of water contaminated by organic and inorganic matter which is dissolved in the water as well as organic and inorganic matter which is not dissolved, namely suspended in the water. The latter-type contaminant may be divided into two groups of materials, those which are settleable in the water and those which are not settleable and tend to float on top of the water. The function of any sewage treatment system is to separate substantially all the suspended matter from the water as well as to greatly reduce the organic matter dissolved therein, and thereafter dispose of the separated matter.
The separated contaminants which are mixed with some water and therefore are in slurry form, often referred to as sludges, are biologically active until stabilized by subsequent treatment. The stabilization is generally achieved by biological digestion. Such digestion is sometimes used to produce combustible gases such as methane, useful as a source of energy. However, the remaining solid material presents difficult and costly disposal problems. Digested (humic) solids have been processed to fertilizers and soil conditioners. This practice is generally not economical and the quantity available greatly exceeds the market demands. Municipalities are finding it increasingly difficult to dispose of the remaining sludge solids in waterways, oceans or landfills, due to their ecological impact. Legislation is being considered to reduce and eventually forbid such solid dumping. Thus, disposal of solids, produced by prior art treatment systems, present a very severe problem, in addition to the high disposal cost. Other disadvantages of prior art systems in which biological digestion is employed include the large land area of aeration basins required for their operation, and the releasing of offensive odors. Also, prior art systems are relatively inefficient and must be carefully monitored and controlled to prevent any unbalancing in the biological digestion. That is, the types and/or amounts of contaminants per liter of water must be controlled to be within specified limits in order not to upset the biological digestion process.
An attempt to reduce the amount of solids requiring disposal is described in U.S. Pat. No. 3,640,820. Therein, a sewage treatment process is described in which the sewage sludges are converted into an active material which is used in the process. Several disadvantages of the system described in said patent are apparent. The proposed process is one employing biological digestion and therefore suffers from all of the shortcomings, hereinbefore discussed. In addition, it requires the use of a conditioning agent in the active material production.
In the Feb. 22, 1972 issue of Chemical Engineering, a process developed by DuPont and known as PACT for Powdered Activated Carbon Treatment is disclosed. Therein, activated carbon, which is not produced from contaminants in liquid waste is required, thereby increasing process costs. Also, the amount of material, requiring final disposal, is not reduced and therefore the disposal cost is high and the disposal problems are not solved.